The present invention relates to a lock-up control device of a torque converter used for an automatic transmission.
A torque converter drives a turbine by oil stirred by an impeller, and transmits power by hydraulic power transmission. Although the torque converter increases torque and absorbs torque fluctuations, slip occurs between the impeller and turbine, so efficiency of the transmission decreases.
In a lock-up torque converter, the slip can be eliminated and efficiency of the transmission can be increased by locking the impeller and turbine by engaging a lock-up clutch in a running region where torque increase and absorption of torque fluctuation is unnecessary.
The torque converter disclosed by JP-A-H5-79560 published by the Japanese Patent Office in 1993 discloses a torque converter comprising a lock-up control chamber partitioned by a lock-up clutch piston from a converter chamber. When a lock-up control pressure is supplied to this lock-up control chamber, the lock-up clutch piston displaces so that the lock-up clutch is engaged, and the impeller and turbine are locked. This torque converter is a three circuit lock-up torque converter comprising an inlet circuit which supplies oil to the torque-converter chamber, an outlet circuit which discharges oil from the torque-converter chamber, and a lock-up control circuit which supplies lock-up control pressure to the lock-up control chamber.
In the three circuit torque converter, when the lock-up clutch piston receives the lock-up control pressure in the lock-up control chamber and locks the impeller and turbine, the lock-up piston must be displaced against the converter pressure in the converter chamber. Therefore, if the lock-up control pressure is not a value obtained by adding a pressure corresponding to the resistance due to the converter pressure to the pressure corresponding to the required engaging capacity of the lock-up clutch, the required lock-up clutch engaging capacity will not be obtained.
Therefore, the lock-up control pressure must always be controlled according to the converter pressure, and this control must be performed precisely regardless of variation in the source pressure.
It is therefore an object of this invention to arrange that there is no insufficiency of engaging force of the lock-up clutch even if there is a pressure difference between the converter pressure and an inlet/outlet pressure of a converter.
In order to achieve above object, this invention provides a lock-up control device for controlling a lock-up clutch in a torque converter, the lock-up clutch being engaged by supplying a lock-up control pressure, and the torque converter transmitting torque via a fluid in a torque converter when the lock-up clutch is disengaged and transmitting torque directly when the lock-up clutch is engaged. The lock-up control device comprises an inlet circuit which supplies fluid to the torque converter chamber, an outlet circuit which discharges fluid from the torque converter chamber, a signal output device which outputs a signal pressure according to a required engaging capacity of the lock-up clutch, and a lock-up control valve which outputs a lock-up control pressure according to the signal pressure. The lock-up control pressure which is fed back is input to the lock-up control valve to decrease the lock-up control pressure, and the pressures in the inlet circuit and outlet circuit are input to the lock-up control valve to increase the lock-up control pressure.
According to an aspect of the invention, this invention provides a lock-up control device for controlling a lock-up clutch in a torque converter, the lock-up clutch being engaged by supplying a lock-up control pressure, and the torque converter transmitting torque via a fluid in a torque converter when the lock-up clutch is disengaged and transmitting torque directly when the lock-up clutch is engaged. The lock-up control device comprises an inlet circuit which supplies fluid to the torque converter chamber, an outlet circuit which discharges fluid from the torque converter chamber, a signal output device which outputs a signal pressure according to a required engaging capacity of the lock-up clutch, and a lock-up control valve which outputs a lock-up control pressure according to the signal pressure. The pressure of the inlet circuit, the pressure of the outlet circuit and the lock-up control pressure which is fed back, are input to the lock-up control valve. The lock-up control valve increases the lock-up control pressure when the pressure of the inlet circuit and pressure of the outlet circuit increase, and decreases the lock-up control pressure when the lock-up control pressure which is fed back increases.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.